This application relates to a process for the preparation of organic acid chloride, more particularly it relates to a process for preparation of an organic acid chloride selected from alkyl and aryl organic acid chlorides and, particularly, to the preparation of acetyl chloride, benzoyl chloride and toluoyl chloride.
Many organic synthesis employ acid chlorides in their reactions. For example, acetyl chloride is used on a large scale as a catalyst in the chlorination of acetic acid. Usually in such cases, it is made in situ from acetic anhydride and by-product hydrogen chloride from the chlorination reaction. Unfortunately, in such processes only one-half of the available acetyl groups are utilized for the acetyl chloride, the remainder going to acetic acid. Acetyl chloride is a powerful acylating agent when used with aluminum chloride catalyst and will acetylate many compounds which cannot be acetylated with acetic acid or acetic anhydride. Acetyl chloride is also employed in the preparation of acetanilide, acetophenone and other industrial acetyl derivatives including anhydrides of carboxylic acids.
Several methods are known for preparation of organic acids, particularly acetyl chloride. According to Kirk-Othmer, Encyclopedia of Chemical Technology, Second Edition, Vol. 1, pages 138-142, acetyl chloride has been prepared by the action of chlorinating agents on acetic acid, its salts, esters or anhydrides, as indicated above by conveniently treating acetic anhydride with hydrogen chloride in situ. Although the foregoing method is used industrially for in situ production, normal laboratory preparations involve slow addition of phosphorus trichloride to acetic acid with cooling. Commercially, acetyl chloride is prepared by treating sulfur dioxide and chlorine with sodium acetate, followed by distillation.
In an article by Montonna, JACS, Vol. 49, pages 2114-2216 (1927), there is described a method for preparation of acid chlorides in which silicon tetrachloride is reacted with acetic acid or other appropriate organic acid at 50.degree.-60.degree. C. in various solvents to produce the organic acid chloride. The advantage of this reaction is indicated to be the preparation of "phosphorus- and sulfur-free" acid chlorides by the action of silicon tetrachloride on a corresponding organic acid. Yields of from about 50% up to 85% for acetyl chloride are given in various solvents such as aromatic hydrocarbons and ethers, although subsequent literature indicates Montonna's data to be suspect.
Although the Montonna method produces "phosphorus- and sulfur-free" organic acid chlorides, it suffers from the disadvantages of incomplete utilization of raw materials, production of complex by-products and evolution of much HCl.
Also, Dandegaonker, CA Vol. 62, 2700 (1965), is reported as reacting silicon tetrachloride with carboxylic acids, anhydrides and acid salts to give tetracetyloxysilanes and HCl, acyl chlorides and sodium chloride, respectvely. Decomposition of the tetracetyloxysilanes at greater than 200.degree. C. was reported to yield the anhydrides. Further, Udovenko et al, CA Vol. 52, 3712D (1958), is reported to have reacted silicon tetrachloride with excess acetic anhydride to yield a precipitate of 80% silicon tetraacetate and acetyl chloride. The same products formed with other proportions of reactants but the products failed to precipitate if the ratio is under 1:4 silicon tetrachloride to acetic anhydride.
Benzoyl chloride may be prepared in many ways according to Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd Edition, Vol. 3, p. 430-431, Interscience Publishers, New York (1964). For example, the partial hydrolysis of benzotrichloride; the chlorination of benzaldehyde and the reaction of benzoic acid with phosphorus pentachloride, phosgene or benzotrichloride, all afford benzoyl chloride. Large scale manufacture of benzoyl chloride for use as a benzoylating agent by which the benzoyl radical is introduced into alcohols, phenols, amines and other compounds through the Friedel-Crafts reaction and the Schotten-Baumann reaction are known. These reactions produce benzoyl peroxide, benzophenone, benzyl benzoate and other derivatives which have end uses in the dye, resin, perfume, pharmaceutical and polymerization catalyst fields. Toluoyl chloride has similar uses and can be produced in a similar manner from corresponding raw materials. In addition, the reaction of toluic acid with sulfonyl chloride or phosphoryl chloride also produces toluoyl chloride.
In view of this, the art has a need for an inexpensive organic acid chloride which is nevertheless free of sulfur- and phosphorus-containing residues. Such compounds would enjoy wide acceptance in the pharmaceutical industry.